In a conventional floating roof tank, with which the seal of the invention is particularly useful, there is provided a clearance space or rim space between the tank side wall and the vertical rim or wall of the roof. It is necessary to provide such clearance space to permit unrestrained vertical travel of the roof within the tank. The clearance space is of sufficient size that local dimensional variations in the circularity of the tank sidewall or shell, commonly called out-of-roundness, which can result from uneven foundation settlement, imprecise fabrication or erection or unusual live loads such as high winds and the like, do not hamper vertical travel of the roof.
A conventional system for centering a floating roof in a tank and simultaneously sealing the space between the roof rim and the tank inner side wall employs as a sealing means a yieldable annulus suspended by the roof and extending from contact with the roof rim into contact with the tank wall. The annulus can be made of flexible sheet material and can contain a fluid, i.e. liquid or gas, such as water or nitrogen, or a resilient material such as a polymeric foamed material. U.S. Pat. Nos. 3,136,444; 3,120,320; 3,075,668; 3,055,533; 2,973,113 and 2,968,420 illustrate seals of those types.
Other apparatus to maintain the roof centered in the tank and to effect a seal against evaporation loss uses a plurality of vertical shoes adapted to slidably contact the entire circular inner side wall of the tank and means supported by the roof for pressing the shoes against the inner side wall, as well as to support the shoes. Vapor loss between the roof and shoes is prevented by a flexible vapor resistant fabric barrier which extends from the upper part of the shoes to the floating roof top edge. Such apparatus is disclosed in many U.S. Pat. Nos. including 2,587,508; 2,630,937; 2,649,985 and 2,696,930.
Many floating roof storage tanks are erected at great distances and at places remote from manufacturing centers around the world. This makes it necessary to transport all the components at great cost because of the labor and shipping costs involved. Because of this, it is desirable if an improved vapor space seal not only seals properly but desirably also employs components which are low cost, readily shipped and transported, easily assembled and quickly installed.
Glass U.S. Pat. No. 1,674,038 discloses a floating roof storage tank which uses a plurality of tubular sections as a seal which bridges the space between the tank wall and the roof top edge. The tubular sections are not located between the roof wall and the tank wall so that they cannot exert a centering action on the roof. Instead, the tubular sections rest on a flange slanted upwardly and inwardly from the roof upper edge. The tubular sections, in one version, are inflated with air and internally weighted with gravel, shot or some other material, to wedge the tubular sections between the flange and the tank wall. FIG. 3 of the reference shows tubular sections with springs therein, with the springs stated to have the same effect in holding the tubes distended that air has.